1. Field of the Invention
The present invention has to do with surgical fasteners which are implanted in the body. In particular, the invention has to do with improved surgical fasteners which expand when they are implanted in a patient. The expansion stabilizes the fastener in the patient.
2. The Related Art
Expansion fasteners such as the Molly® expansion bolt sold by The Black & Decker Corporation are known in the fastener art. Applicants have now discovered that fastener products employing similar principles can be modified in new ways for use as surgical implants.
Bone, except in the skull, has an outside cortical shell which is hard and strong with an average thickness from about 0.05-0.4 millimeters (“mm”). The portion of the bone under the cortical shell is cancellous and is a much softer material. This characteristic of bone structure creates problems in surgery. Conventional surgical screws, for example, can loosen and become unstable, for example, they may rotate over time and pull out requiring re-surgery. They can also break or become infected and have to be removed. They may be overtightened causing the bone to be stripped out or the patient may have weak bone tissue or bones weakened by disease such as osteoporosis so that the bones are not strong enough to hold the screw. These problems and many others are solved by the fasteners of the present invention.